1. Field of the Invention
The present inventions relates to corrosion protection and increased adhesion between substrates and a subsequent bonded material. More specifically, the present invention is related to primers, manufactured from at least one organofunctional bis-silane, having increased film thickness, chemical and scratch resistance, as well as being substantially chromate-free and comprising little to no VOCs.
2. Background of the Invention
In recent years, organofunctional silanes have been shown to be powerful systems for protecting a wide range of metals against corrosion when applied as primers. The adhesion of paint is drastically improved when organofunctional silanes are applied as a primer pretreatment. Adhesion and adhesion durability of metals to rubber compounds and structural adhesives have also been objectives of prior art organofunctional silanes systems.
When used as a corrosion protection treatment without paint, prior art silane films have limitations in that the film thickness is not more than 0.3 μm. Such films provide remarkable protection so long as they are not scratched or otherwise damaged. Also, it has been very difficult to apply a thin silane film without pinholes or other defects appearing in the film. In addition, prior art silane films have been transparent and colorless, thereby providing little visual detection as to defects in the film. Consequently, prior art silane films applied alone provided only temporary protection of metals and, therefore, there is a need for metal treatment systems that meet or exceed the following criteria* which prior art silane films cannot meet entirely:                1. the film thickness should range from 1 to 20 μm;        2. the coating should cure in air or thermally at slightly elevated temperatures;        3. the coating should withstand deep drawing;        4. the coating should adhere very well to metals and should be paintable by all common paint systems such as epoxies, polyesters, acrylates, polyurethanes and the like;        5. the coating should have a high UV resistance so that it can be used externally without overcoating;        6. the compounds used in the coating should all be water soluble or dispersible; it should be a low VOC system (Volatile Organic Compound);        7. the coating should be applied by dipping, wiping, spraying, brushing, and other well known applications methods;        8. the coating should not be completely transparent but opaque and have a color, so that the metal can still be observed but the film can be detected visually; and        9. the coating should have a high thermal stability (it should be stable to at least 250° C. for one hour).It is to be understood that the above “criteria” do not constitute limitations upon the scope of the present invention. One of ordinary skill will surely understand that a silane compound may come within the scope of the present invention even though it fails to meet one or more of the above “criteria”.        